1. Field of the Invention
The present invention relates to an apparatus for improving the sharpness of an image, and more particularly, to an apparatus for improving the sharpness of an image, which may apply an active weight in accordance with a two-dimensional (2D) high pass filtering value of the image, thereby preventing the occurrence of image distortion in an edge enhancement process of the image.
2. Description of the Related Art
In general, the human visual sensation, capable of recognizing an image displayed by an image apparatus, may prefer an image having high sharpness. To satisfy the preference of the human visual sensation, various image sharpness improvement schemes which may be applied to an image apparatus such as a digital camera, a television (TV), a mobile phone equipped with a camera, and the like may be adopted. Of the image sharpness improvement schemes, an edge enhancement scheme in which an existing edge (contour) of a digital image is more enhanced may be widely used.
As a typical edge enhancement scheme, a scheme in which a filtering value generated by applying two dimensional (2D) high pass filtering (HPF) to an entire image is applied to an original image and a scheme in which a filtering value generated by applying 2D-HPF based on each of ascertained characteristics of an edge (for example, directivity) is applied to the original image may be proposed.
In the former edge enhancement scheme, 2D-HPF may be applied to the entire image, and then the entire image may be added to the original image. However, excessive edge enhancement may be carried out in a part having a strong edge element, leading to the occurrence of overshooting and undershooting, thereby causing a ringing phenomenon in which a white edge is generated in an edge region of an object. Also, even minute blurring (background noise) occurring in a flat region of the image due to internal noise of the image apparatus may be enhanced, thereby making the image unnatural.
In the latter edge enhancement scheme, directivity, which is one of the characteristics of the edge, may be ascertained, and a 2D-HPF scheme suitable for the directivity of each of the edges may be selectively applied. Specifically, the edge directivity such as a horizontal direction, a vertical direction, a left diagonal direction, a right diagonal direction, no-directivity, and the like may be ascertained, a 2D-HPF scheme suitable for each of directivities may be selectively applied to generate a filtering value, and the generated filtering value may be applied to the input image. In the latter edge enhancement scheme, the 2D-HPF differing depending on a priority for a type of an ascertainment formula and an ascertained result and depending on the directivity may be required along with an increase in a number of types of the edge directivity, and thereby a size of a system for the edge enhancement may be increased. Also, in the latter edge enhancement scheme, an intensity of the ascertained edge may not be considered although the edge directivity may be ascertained, and therefore a ringing phenomenon may occur in a strong edge part, similar to the former edge enhancement scheme. Also, since 2D-HPF schemes which are different from each other, depending on the directivity thereof, may be applied for each pixel, discontinuous edge enhancement may be carried out, causing a problem in a natural sharpness improvement.
Accordingly, there is the need for a method for preventing an image quality-deterioration phenomenon such as distortion or ringing occurring when the edge enhancement scheme is applied for the purpose of an improvement in the sharpness of an image.